In recent years, the digital watermark technology has become popular for the purpose of embedding information in digital contents such as videos. For example, in conventional technology 1, a technology is disclosed in which digital watermark information is embedded in a video, and a user captures the video using a dedicated camera of a smartphone or the like and extracts the information embedded in the video.
If conventional technology 1 is implemented in a lighting device such as a projector, it is possible to think of a business model in which a light having digital watermark information embedded therein is projected and the smartphone of a user is instructed to detect the information embedded in the projected light.
In the case in which a lighting device projects a plurality of lights having different sets of digital watermark information embedded therein, when the areas of projection of the lights come close to each other, the sets of digital watermark information interfere with each other thereby leading to a decline in the detection accuracy of the information embedded in the lights. In order to deal with that issue, conventional technology 2 and conventional technology 3 are available.
FIG. 25 is a diagram for explaining conventional technology 2. As illustrated in FIG. 25, at the time of emitting a light in which digital watermark information is embedded, and projecting an image 11; a lighting device 10 superimposes a frame 11a onto the image 11. As a result of superimposing the frame 11a, the target area for information extraction becomes clear.
FIG. 26 is a diagram for explaining conventional technology 3. In conventional technology 3, a moving image is divided into small areas, and bit determination is performed based on the luminance variation in each small area. In the example illustrated in FIG. 26, small areas 20a and 20b are formed; and bit determination regarding the small area 20a is performed based on the luminance variation thereof, while bit determination regarding the small area 20b is performed based on the luminance variation thereof.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2012-142741
Patent Literature 2: Japanese Laid-open Patent Publication No. 2005-277732
Patent Literature 3: Japanese Laid-open Patent Publication No. 2003-179556
However, in the conventional technology described above, when a plurality of sets of image data is emitted with embedding information embedded therein and when different sets of embedding information interfere with each other, the area onto which only particular embedding information is superimposed cannot be identified and thus information cannot be obtained.
For example, conventional technology 2 is effective in the case in which only a single light is emitted. However, if a plurality of images gets superimposed, there are times when a plurality of frames is generated. In such a case, it is not possible to identify the area onto which only particular embedding data is superimposed. Moreover, in conventional technology 2, since a frame is superimposed onto an image, it causes disfigurement too.
In conventional technology 3, it is assumed that the embedding information has a high degree of strength. Thus, when there is only minute variation per area as is the case in the digital watermarking technology, it becomes difficult to read information from small areas. For that reason, the signal range of each area needs to be identified and detection needs to be performed using the variation preferably over a wider area. However, in conventional technology 3, it is not possible to resolve such issues.